Fluid is a template engine which lets you display content on a website
very easily. A specific file (the template) will be processed and the
containing placeholders will be replaced with the current content. This is
the basic concept of template engines - as well as Fluid’s.

Fluid is based on three conceptual pillars which build the backbone of
the template engine and provide for scalability and flexibility:

Object Accessors output the content of variables which were assigned to the View to be displayed.

ViewHelpers are special tags in the template which provide more complex functionality such as loops or generating links.

A template engine uses a placeholder to fill content in specified
areas in a template and the result is then returned to the user. In Fluid,
these placeholders are called Object
Accessors.

Tip

The markers used in the classic marker based templates of TYPO3 v4
are also placeholders which are replaced later on by the desired data.
You will notice though, that the placeholders used in Fluid are clearly
more flexible and versatile.

Object Accessors are written in curly brackets. For example,
{blogTitle} will output the content of the variable
blogTitle. The variables have to be assigned in the
controller with $this->view->assign(variableName,object).
Let us look at this in an example of a list of blog posts.
In the controller, we assign some data to the template with the following
code:

Upon generation of the output, the Object
Accessor {blogTitle} will be replaced by the title of the
blog »Webdesign-Blog«. To output the individual blog posts, the tag
<f:for> is used, which you can also see in the template
above. Depending on the title of each blog post, the complete output looks
like this:

If you want to output an object instead of a String, the object
needs to have a __toString()-method which returns the
textual representation of the object.

In the example above, you will also find the Object Accessor
{post.title} which is used to output the title of a blog
post. This hierarchical notation is a syntax that makes it possible to
walk through associations in the object graph - you can literally move
from object to object. Often, a complex object is assigned to the View,
but only parts of it will be displayed. In the example above, we used
{post.title} to display the property title of
the object. Generally, Fluid tries to handle such hierarchical properties
in the following order:

If post is an array or an object which implements the interface ArrayAccess,
the corresponding property will be returned as long as it exists.

If it is an object, and a method getTitle() exists,
the method will be called. This is the most common use case of an Object Accessor,
since by convention all public properties have a corresponding get-method.

The property will be returned if it exists in the object and it
is public. We discourage the ability to utilize this though, since it
violates the Uniform Access Principle (see box)

The Uniform Access Principle

The Uniform Access Principle says, all services offered by a
module should be available through an uniform notation which does not
betray whether they are implemented through storage or through
computation. <remark>Explanation on Wiki</remark>

Stored objects are being accessed directly using public class
variables in PHP - and it is visible on the outside that the object
isn’t being computed. For this reason, we often use get and
set-methods in our models. Therefore, all options of the class are
accessible through method calls and are uniformly addressed - it is
not visible on the outside whether the class computed or stored the
value directly.

You can navigate through more complex objects, because Object
Accessors can be nested multiple times. For example, to output the email
address of an author of a blog post, you can use
{post.author.emailAddress}. That’s almost equivalent to the
expression $post->getAuthor()->getEmailAddress() in
PHP, but focused on the essential.

Only the get-method, and not just any method, of an object can be
called with Object Accessors. This ensures that there is no PHP code in
the template. It is better to place PHP code in your own ViewHelper if
needed. The following describes how to do this.

Functionalities that exceed the simple output of values have to be
implemented with ViewHelpers. Every ViewHelper has its own PHP class. Now,
we’re going to see how we can use ViewHelpers. Later, you’ll also learn
how to write your own ViewHelper.

To use an existing ViewHelper, you have to import the
Namespace and assign a shortcut to it. You can do
this with the declaration {namespace...=...}.

All Namespaces used in your template must always be registered. This
might seem redundant, but because all important information is embedded in
the template, readability increases immensely for other template editors
who work on the same templates.

The standard ViewHelper of Fluid will be imported and assigned to
the shortcut f with the following declaration:

{namespacef=TYPO3\CMS\Fluid\ViewHelpers}

This Namespace will be imported automatically by Fluid. All
ViewHelpers that come with Fluid are prefixed with f. Your
own Namespaces have to be imported into the template like previously
mentioned.

All tags, which begin with a registered prefix, will be evaluated.
Here’s a small example:

Tags without a registered prefix (in this example
<ul> and <li>) will be treated as text. The tag
<f:for> will be interpreted as a ViewHelper since it
starts with the prefix f:. This is implemented in the class
\TYPO3Fluid\Fluid\ViewHelpers\ForViewHelper.

The first part of the class name is the complete Namespace like it
was defined earlier with {namespacef=TYPO3\CMS\Fluid\ViewHelpers}.
Followed by the name of the ViewHelper and the ending
ViewHelper.

Every argument of a ViewHelper will be interpreted by Fluid. The
ViewHelper <f:for> from the previous example therefore
receives the array of all blog posts with the argument
each.

Tip

If the name of the ViewHelper contains a single or multiple
periods, it will be resolved as a sub package. For example, the
ViewHelper f:form.textfield is implemented in the class
\TYPO3\CMS\Fluid\ViewHelpers\Form\TextfieldViewHelper.
Therefore ViewHelpers can be divided further and structured even
more.

ViewHelpers are the main tools of template editors. They make it
possible to have a clear separation of template and embedded
functionality.

Tip

All control structures like if/else or
for are individual ViewHelpers in Fluid and not a core
language feature. This is one of the main reasons for the flexibility
of Fluid. You’ll find a detailed reference of the ViewHelpers in
Appendix C.

It is intuitive and natural for most of the ViewHelpers to be called
with the tag based syntax. Especially with control structures or form
elements, this syntax is easily understood. But there are also ViewHelpers
which can lead to difficult to understand and invalid template code when
used as a tag. An example of this is the f:uri.resource
ViewHelper, which returns the path to a resource in the
Public/ folder of an Extension. It is being used
inside of <linkrel="stylesheet"href="..."/> for
example. Using the normal, tag based syntax it looks like this:

<linkrel="stylesheet"href="<f:uri.resource path='myCss.css' />"/>

That is very difficult to read and doesn’t communicate adequately
the meaning of the ViewHelper. Also, the above code is not valid XHTML and
therefore most text editors can’t display the code with correct syntax
highlighting anymore.

For that reason, it is also possible to call the ViewHelper
differently, with the help of the inline notation.
The inline notation is function-oriented, which is more suitable for this
ViewHelper: Instead of <f:uri.resource/> you can also
write {f:uri.resource()}.

So the example above can be changed to:

<linkrel="stylesheet"href="{f:uri.resource(path: 'myCss.css')}"/>

The purpose of the ViewHelper is easily understandable and visible -
it is a helper function that returns a resource. It is well formed XHTML
code as well and the syntax highlighting of your editor will work
correctly again.

We’ll illustrate some details of Fluid’s syntax, based on formatting
a date.

Lets assume we have a blog post object with the name
post in the template. It has, among others, a
property date which contains the date of the creation
of the post in a DateTime object.

DateTime objects, that can be used in PHP to
represent dates, have no __toString()-method and
can therefore not be outputted with Object Accessors in the template.
You’ll trigger a PHP error message, if you simple write
{post.date} in your template.

In Fluid there is a ViewHelper f:format.date to output
DateTime objects, which (as you can see on the prefix
f:) is already part of Fluid:

<f:format.dateformat="Y-m-d">{post.date}</f:format.date>

This ViewHelper formats the date as defined in the
format property. In this case, it’s very important
that there are no whitespaces or newlines before or after
{post.date}. If there is, Fluid tries to chain the whitespace
and the string representation of {post.date} together as
string. Because the DateTime object has no method
__toString(), a PHP error message will be thrown
again.

Tip

To avoid this problem, all f:format-ViewHelpers
have a property to specify the object to be formatted.

Instead of writing
<f:format.date>{post.date}</f:format.date>
you can write: <f:format.datedate="{post.date}"/>
to bypass the problem. But again, there can’t be any characters before
or after {post.date}.
</tip>You can pretty much see, that in this case the tag based syntax is
prone to errors: We have to know, that {post.date} is an
object so we don’t add whitespaces inside of
<f:format.date>...</f:format.date>.

An alternative would be to use the following syntax:

{post.date->f:format.date(format:'Y-m-d')}

Inside the Object Accessor we can use a ViewHelper to process the
value. The above example is easily readable, intuitive and less error
prone as the tag based variation.

Tip

This might look familiar, if you happen to know the UNIX shell:
There is a pipe operator (|) which has the same functionality as our
chaining operator. The arrow shows the direction of the data flow
better though.

You can also chain multiple ViewHelpers together. Lets assume we
want to pad the processed string to the length of 40 characters (e.g.
because we output code). This can be simply written as:

The data flow is also easier to read with an inline syntax like
this, and it is easier to see on which values the ViewHelper is working
on. We can thus confirm that you can process the value of every Object
Accessor by inserting it into the ViewHelper with the help of the chaining
operator (->) . This can also be done multiple times.

Arrays round off the concept of Fluid and build another core concept
of the template engine. Arrays in Fluid can be somewhat compared to
associative arrays in PHP. Every value in a Fluid array needs a
key.

Arrays are used to pass a variable number of arguments to View
Helpers. The best example is the link.action-ViewHelper. With
this you can create a link to other Controllers and Actions in your
Extension. The following link refers to the index Action of
the Post Controller:

Many links in your application though need parameters, which can be
passed with the arguments attribute. We can already see that
we need arrays to do so: It’s unpredictable how many parameters you want
to pass. By using an array we can pass an indefinite amount of parameters.
The following example adds the parameter post to the
link:

The array {post:currentPost} consists of a single
element with the name post. The value of the element is the
object currentPost. Multiple elements are separated by a
comma: {post:currentPost,blogTitle:'Webdesign-Blog'}.

Fluid only supports named arrays, which means, that you always have
to specify the key of the array element. Lets look at what options you
have when creating an array:

The array can contain strings as values as in key1 and key2.
It can also have numbers as values as in key3. More interesting are key4
and key5: Object Accessors are being specified as array values. You can
also access sub-objects like you are used to with Object Accessors. All
strings in arrays are interpreted as Fluid markup as well. So that you can
combine strings from individual strings for example. This way, it is also
possible to call ViewHelpers with the inline notation.

These are the basic concepts of Fluid. Now we move on to more
advanced concepts, which increase the effectiveness of template creation.
The following chapter will explain how to use different output formats to
achieve different views of data.